Abstract: On the basis of water-drive experiments with the micromodel of true sandstone,the water-drive mechanism and characteristics of the Ansai Chang-6 supertight reservoir after water-occurrence is observed and analyzed.It is considered that the Jiamin Effect exert a notable influence on the water-drive efficiency after water-occurrence,and is characterized by the increase of injection resistance and pressure.With the rising of injection pressure,the water-flow pathway formed before is "deadlocked" after injected water forms new seepage pathways,the oil drops left in pore throats only deform and are difficult to migrate under the impact of additional capillary resistance.Affected by the anisotropy of reservoir pore structure,the seepages of fluid in the Chang-6 reservoir only have effects on part well-interconnected macro-pores.When injected water is 0.5-0.8 times of pore volume,water occurs in all oil wells.the continuous jaming-colesing-rejaming process of the oil drops left in water-flushing pathways under hydrodynamic action is one of the ways to raise the oil-expulsive efficiency after water-occurrence.The water-drive patterns in fissure-developing zones mainly depend on whether pore permeability,fissure permeability and displacement pressure are high or low.